Statement of the Invention
The invention relates to an over-voltage circuit for a phase controlled regulator and, more particularly, to an over-voltage circuit which places the regulator in a continuous off/on mode in response to an over-voltage as long as the over-voltage persists.
The main function of prior art over-voltage interrupt arrangements has been to shut down to protect the subsequent circuitry from destructive over-voltages. Accordingly, the over-voltage interrupt circuits have consisted of what are popularly known as "crowbar" circuits which short circuit the output voltage of the regulator in response to an over-voltage and perhaps trip a circuit breaker. A popular "crowbar" element has been a silicon controlled rectifier (SCR) which is tied directly across the outputs of the regulator. There are a number of disadvantages of this type of over-voltage interrupt circuitry, such as the necessity of manually resetting the circuit breaker. These type circuits, for all practical purposes, are fast in order to protect the load from damage or destruction. However, the "crowbar" requires an adjustment to speed in order to prevent a large number of nuisance trips due to noise.
Earlier attempts have been made to limit the output voltage of the regulator in response to an over-voltage condition by turning the gate pulse on and off directly in the case of a silicon controlled rectifier (SCR) phase controlled regulator. However, large voltage excursions were experienced at the output of the regulator.